By way of example, the optical system referred to above is used in a telescope or in field glasses. The image captured by an observer through the telescope or field glasses is often perceived to be shaking because trembling movements or rotational movements of the hands of the user, and also movements underfoot, in turn cause movements of the optical system. In order to avoid this, it is known to stabilize images in an optical system. Known solutions use stabilizing apparatuses for stabilizing the image by means of a mechanical apparatus and/or an electronic apparatus. Furthermore, so-called passive stabilizations and active stabilizations are known, as will still be explained in more detail below.
A passive stabilization is known from DE 23 53 101 C3. This document describes an optical system in the form of a telescope, which has an objective, an image stabilizing unit in the form of a prism erecting system and an eyepiece. As seen in the direction of the eyepiece from the objective, the objective is arranged first along an optical axis of the optical system, then followed by the image stabilizing unit and then followed by the eyepiece. The prism erecting system is mounted in cardan-joint fashion in a housing of the telescope. This is understood to mean that the prism erecting system is arranged in the housing of the telescope such that the prism erecting system is rotatably mounted about two axes arranged at right angles to one another. For the rotatable mounting, use is made of a device which is referred to as a cardan suspension. The two aforementioned axes intersect at a hinge point. In the case of the known optical system, provision is now made for arranging the hinge point centrally between an image-side main plane of the objective and an object-side main plane of the eyepiece. The prism erecting system, mounted in a cardan-joint fashion, is not moved by occurring rotational-trembling movements as a result of its inertia (passive stabilization). It therefore remains fixed in space. This is how image shaking which occurs as a result of the rotational-trembling movement of the housing is compensated for.
By way of example, an active stabilization has been disclosed in DE 39 33 255 C2. This document has disclosed binocular field glasses with an image stabilization having a prism erecting system. The prism erecting system has Porro prisms, which respectively have one tilt axis. The Porro prisms are designed such that they can pivot about their respective tilt axis. Motors are provided for pivoting the Porro prisms (active stabilization). The pivoting is brought about dependent on a trembling movement, which causes a shaking of an observed image such that image deterioration is avoided.
A further example of a known passive stabilization is disclosed in DE 28 34 158 C3. This document discloses a telescope with an arrangement consisting of an objective, a prism erecting system and an eyepiece, wherein provision is made for two partial telescopes, which each have one instance of the aforementioned arrangement. The prisms of the prism erecting systems of the two partial telescopes are mounted in a common cardan suspension in a housing. The hinge point lies in the center between the image-side main plane of the objective and the object-side main plane of the eyepiece. Moreover, the hinge point lies in the center of gravity of the cardan suspension. However, it has now been found that in the case of telescopes with a magnification of greater than 8, each of the prism erecting systems is arranged closer to the corresponding eyepiece than to the respective objective. So that each prism erecting system in the cardan suspension is in equilibrium it is necessary to provide at least one counterweight. However, the use of a counterweight is not necessarily desirable because this increases the weight of the telescope.
In order to avoid the use of a counterweight, use can for example be made of an active stabilization, as already described further above. Then it is no longer necessary to place the hinge point of the prism erecting system in the center between the image-side main plane of the objective and the object-side main plane of the eyepiece. Rather, the position of the hinge point can be freely selected on the optical axis of the optical system. However, if the hinge point is closer to the eyepiece than to the objective, it was found that the prism erecting system should be tilted against the tilt of the housing by an angle (prism tilt angle) which is greater than the magnitude of the angle of the tilt of the housing. The prism tilt angle of the tilt relative to the objective and relative to the eyepiece in addition to the trembling movement causes an aberration in the form of coma for the imaging of an object, and so the image quality is reduced. Accordingly, the prism erecting system produces this coma. However, deterioration in the image quality is undesirable.
U.S. Pat. No. 6,067,194 has disclosed a further optical system with a passive stabilization. This known optical system has an objective, an erecting system and an eyepiece. The erecting system has a plurality of elements. Thus, it has a deflection mirror, a Schmidt prism and a prism for 180° deflection. The eyepiece and the prism for 180° deflection are fixedly connected to a housing and are co-moved as a result of a trembling movement of a user. The Schmidt prism and a lens with negative refractive power are arranged as a single assemblage such that they can pivot about a horizontal axis. In the assemblage itself a vertical axis is realized in turn, about which a further assemblage consisting of the objective and the deflection mirror can be pivoted. For the purposes of image stabilization, provision is made for pivoting the Schmidt prism and the lens with negative refractive power about the horizontal axis by virtue of the inertia thereof. Moreover, the objective and the deflection mirror can additionally pivot about the vertical axis. The two axes (i.e. the horizontal axis and the vertical axis) do not intersect at a common intersection. Accordingly, this is not a hinge point of a cardan suspension as described above.
Accordingly, it would be desirable to specify an optical system with image stabilization, which firstly dispenses with the use of counterweights and secondly compensates for or prevents the aberrations, in particular coma, introduced by an erecting system.